We propose to study the regulation of the post-replication DNA repair pathway and its associated SOS functions. Specifically we will subclone the recA (and lexA) operon from lambda precA into a suitable vector. We will also fuse the recA control region to a well-characterized structural gene. The recA clone and recA gene fusion will be used in vivo (1) to study regulation of the operon under various conditions, such as those that induce SOS functions and in various mutants, and (2) to examine basic characteristics of recA transcription and translation. The recA clone and recA gene fusion will also be used in vitro and in a cell-free DNA dependent transcription and translation system to identify positive and negative cofactors or proteins which interact with the recA operon.